email to large bcc list get rejected

I have a problem with the sending an email to large bcc list (about 30 emails in the list) from outlook :-

The email :-

to : one recipient
from : an email account on the same server
cc : none
bcc : a list about 30 emails created in outlook on a standalone WinXP with a DSL line (qwest)
incoming/outgoing mail server : mail.userdomain.com